Wire bonding apparatuses are commonly used for connecting a chip and a substrate. Such wire bonding apparatuses include two types: ball wire bonding apparatuses and wedge wire bonding apparatuses. A ball wire bonding apparatus connects a plurality of pads of a chip respectively with a plurality of leads of a substrate by repeating: forming an initial ball from a wire extending from a tip of a capillary by causing a spark and such; bonding the initial ball as a bonding ball to a pad of the chip by pressing the initial ball onto the pad and applying ultrasonic vibration to the initial ball; looping the wire toward a lead of the substrate while paying out the wire from the capillary; bonding the wire by pressing the wire to the lead of the substrate; cutting the wire after moving the capillary upward and extending a wire tail from the tip of the capillary; and forming an initial ball from the wire tail by causing a spark and such for bonding to the next pad.
Further, a wedge wire bonding apparatus uses a tool having a wire feed guide and a pressing surface, and includes the steps of: bonding a wire to a pad of a chip, without forming an initial ball, by pressing a side of the wire to the pad of the chip by the pressing surface while the wire feed guide maintains a direction of the wire and by applying ultrasonic vibration to the wire; looping the wire to a lead of a substrate after raising the tool; bonding the wire to a surface of the lead by pressing the side of the wire by the pressing surface of the tool; cutting the wire by moving the tool obliquely upward toward a connecting direction of the wire; and extending a wire tail under the pressing surface of the tool. Then, a plurality of pads of the chip and a plurality of leads of the substrate are connected respectively by repeating the steps of: moving the tool above the next pad; and pressing and bonding a side of the wire tail extending under the pressing surface to the pad of the chip (see Patent Literature 1, for example).
According to the wedge bonding apparatus described in Patent Literature 1, as the side of the wire is pressed against the pad of the chip by the pressing surface while maintaining the direction of the wire by the wire feed guide, the wire is always required to extend toward the connecting direction of the wire. As the connecting direction between the pad of the chip and the lead of the substrate changes in various directions, however, various methods such as providing a rotary-type bonding head (see Patent Literature 2, for example), or rotating the bonding stage holding the chip and the substrate are employed so as to align the direction of the wire feed guide of the bonding tool with the connecting direction of the wire.
However, rotating the bonding head or the bonding stage poses a problem of increasing a size of a bonding apparatus as a whole, as well as a problem of a slower bonding speed, which results in an inability of high-speed bonding. Therefore, there is proposed a method of bonding a wire to a semiconductor pad and to a lead of a substrate while using a capillary but without forming an initial ball (see Patent Literature 3, for example). The wedge wire bonding method described in Patent Literature 3 proposes a method in which a capillary is moved upward after bonding to a second bonding point and extending a wire tail, then horizontally toward a direction along a succeeding connecting direction of the wire, then downward to a position at which a tip of the capillary is slightly in contact with the wire bonded to the second bonding point, and again horizontally toward the direction along the succeeding connecting direction of the wire to cut the wire tail (see paragraphs 0040 to 0049 of Patent Literature 3). According to this method, the wire tail may be flexed at the tip of the capillary toward the succeeding connecting direction of the wire, and therefore it is possible to perform wedge wire bonding of the wire by pressing the flexed portion of the wire by the tip of the capillary in the succeeding bonding, without rotating the bonding head nor forming an initial ball. In addition, Patent Literature 3 also describes that in the first bonding, wedge wire bonding is performed after forming an initial ball and performing ball wire bonding of the ball at an appropriate position on the substrate, and then causing the wire be flexed in the direction along the succeeding connecting direction of the wire when cutting the wire tail (see paragraph 0050 of Patent Literature 3).